[docs] [issue9182] document “--” as a way to distinguish option w/ narg='+' from positional argument in argparse

Daniel Albeseder <kotan@gmx.at> added the comment: I did the patch for adding the "--" in the generated usage text inside issue 9338. ---------- nosy: +Kotan _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue9182> _______________________________________